HR: 0800h
AN: V11A-0373 INVITED    [Abstracts]
TI: Saucer-shaped Clastic Intrusions and Associated Injectites in the Westerm San Joaquin Valley
AU: * Hurst, A
EM: a.hurst@abdn.ac.uk
AF: University Aberdeen, Dept. Geology & Petroleum Geology, Kings' College, Aberdeen, AB24 3UE, United Kingdom
AU: Vigorito, M
EM: m.vigorito@abdn.ac.uk
AF: University Aberdeen, Dept. Geology & Petroleum Geology, Kings' College, Aberdeen, AB24 3UE, United Kingdom
AU: Vetel, W
EM: Vetelw@cardiff.ac.uk
AF: 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, United Kingdom
AU: Cartwright, J
EM: joe@ocean.cf.ac.uk
AF: 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, United Kingdom
AB: Clastic sills, including saucer-shaped intrusions, are the most volumetrically significant clastic intrusions in the Panoche Giant Injectite Complex (PGIC). Injection occurred in the Lower Paleocene during a period of inversion caused by the convergence of the Pacific and North American plates. Almost 400 km2 of exposure reveals the relationships between clastic intrusions, their parent beds and seafloor sand extrusions (extrudites). Sand was injected into partially-consolidated deepwater mudstones of late Cretaceous and early Paleocene age in a single event but with many pulses that produced cross-cutting intrusions. More than 40 km3 of sand is estimated to have injected within the area of outcrop. The total thickness of strata cut by injections (from deepest known Lower Cretaceous parent bed to extrudite) is in excess of 1.2 km. Saucer-shaped intrusions are composite features that comprise sills, low-angle dikes and dike swarms, arranged as low-angle conical or saucer-shaped injected units that exhibit a semi-elliptical to horse-shoe geometry in plan view and are V- or U-shaped in cross section. Saucer-shaped intrusions are 500 to 1.5km wide and in some cases cut through more than 250 m of stratigraphic section. The lowest parts of the saucer-shaped intrusions consists of multiply-stacked, low-angle dikes up to 80m thick that cut the stratigraphy at angles between 5-10º and locally exhibit stepped or transgressive geometry. The low-angle dykes are 8 to 20 m wide and laterally continuous over distances of a few to several hundreds of metres. Steeper segments (up to 30 deg) emanate laterally from the periphery of the lowest units and cut through the host-rock for a few up to several tens of metres, pinching-out laterally over distances of several tens to a few hundreds of metres. At their margins the saucer-shaped intrusions are bounded by steep (50-70 deg), narrow dikes (generally <1 m wide); such dikes are unlikely to be imaged on seismic data. The central areas of the saucer-shaped intrusions contain uncommon, narrow, widely spaced, thin dikes. Evidence for forced folding and jacking up of the host-rock related to emplacement of the saucer-shaped intrusions is identified Multiple dikes terminate at the base of the saucer- shaped intrusions; the dikes have variable apertures ranging from a few centimetres up to 2 m and are inferred to be feeders of the saucer-shaped intrusions.
UR: http://www.abdn.ac.uk/geology/people/staffpages/hurst/hurst.php#si
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting